A method for manufacturing a molded product by use of a mold has been broadly applied to, for example, mass production of molded products which have a predetermined shape and are made of resin, glass, metal or the like as a main material.
Recently, optical lenses which are made of resin and are used in various electronic devices such as (i) an optical pickup of an optical disk (such as CD or DVD) drive and (ii) a small-sized camera provided in a mobile terminal device have been manufactured by use of molds. Most of the optical lenses are manufactured by (i) applying or pouring a resin (optical polymer) to a mold and then (ii) curing the resin in the mold.
For example, a mobile terminal device can reduce not only its weight and size but also manufacturing cost by employing a lens which has been mass produced by use of a mold. There has been particularly known, as a method for manufacturing a plurality of small-sized lenses, a method for manufacturing a wafer level lens array by applying or pouring a material for lenses, i.e., a resin to arranged molds for molding the lenses. What is meant by “wafer level lens array” is a molded product formed by integrating a substrate part with a plurality of lenses. Generally, the plurality of lenses are connected to each other via the substrate part. The plurality of lenses thus formed can be mass produced by (i) releasing the wafer level lens array from a mold (mold release) and then (ii) separating the wafer level lens array into the plurality of lenses by cutting the substrate part between the respective plurality of lenses.
Meanwhile, according to such a method for manufacturing a wafer level lens array, there may be a case where a wafer level lens array (molded product) cannot be released from a mold because the wafer level lens array strongly adheres to the mold. An external force to be applied to release the wafer level lens array from the mold will, for example, damage the lenses, scratch surfaces of the lenses, or deform spherical surfaces of the lenses (such deformation of the spherical surfaces will cause lens aberration). This may impair optical properties of the lenses. It is therefore significant to smoothly release the wafer level lens array from the mold so as to secure quality and productivity of the lenses.
Patent Literature 1 describes a wafer level lens array manufacturing method including the step of releasing a molded product from a pair of molds by (i) cooling one of the pair of molds while or before the molded product is released from the pair of molds, or (ii) simultaneously cooling and ultrasonically vibrating one of the pair of molds.
Patent Literature 2 discloses a method for molding a resin material into a molded resin product by use of a pair of molds between which the resin material is sandwiched, the method including the step of releasing the molded resin product from one of the pair of molds by decreasing a temperature of the one of the pair of molds by a predetermined temperature.
Patent Literature 3 discloses a method for easily releasing a molded resin product from a casting mold by (i) bringing the molded resin product into direct contact with a planar vibrator, and (ii) transmitting sound or ultrasonic vibrations to the molded resin product and also indirectly to the casting mold.
Patent Literature 4 discloses (i) a mold for press molding an optical lens and (ii) a method for manufacturing an optical lens made of glass, the mold and the method each being used to manufacture a diffraction lens having a plurality of concentric circular bands. The mold has a diffraction effect transfer surface and a stair transfer surface. The stair transfer surface is coarser than the diffraction effect transfer surface. This reduces a stress to be applied to a lens material in releasing the lens material from the mold. It is therefore possible to prevent the glass from adhering to the mold.